This study will investigate the ability of ST101 to improve memory in people with Alzheimer's disease who currently receive 10 mg Aricept® (donepezil) per day. This study also will examine the safety and tolerability of the drug. This study is evaluating 3 different dose levels of ST101 and placebo. Patients will have a 1 in 4 chance of getting placebo. All eligible subjects will be provided with bottles of 10 mg Aricept (donepezil) during the study drug administration part of the study.